To achieve the orientation of a ceramics, a TGG method and an RTGG method are known. In the TGG method, template grains with high anisotropy are arrayed mechanically or by an external field in advance, followed by reacting with matrix grains made of the same composition as that of the template grains for growth. In the RTGG method, the template grains are subjected to reaction with the matrix grains to obtain the oriented grains having a desired composition. Further, in recent years, with the development of a superconducting magnet device, there is proposed a method in which a strong magnetic field of 10 T is developed so that even grains with not particularly high anisotropy can be oriented. In this method, there is proposed, as the orientation using a magnetic susceptibility anisotropy can be conducted, to obtain a compact oriented in a specific direction by applying a rotating magnetic field during a slip cast to a ferroelectric material and a piezoelectric material of a tungsten bronze structure metal oxide, whose crystal axis is short in functional axis and alignment cannot be performed by a mechanical stress such as one obtained by a doctor blade method, (Patent Literature 1).
As a result of extensive study on the oriented ceramics of the tungsten bronze structure metal oxide, it was found that the higher orientation is required for improving the characteristics as a piezoelectric material. That is, in the case of the tungsten bronze structure metal oxide, most of the compositions each have a polarization axis in a c-axial direction except for some lead based materials, and a non-180° domain such as the piezoelectric material of a perovskite-type metal oxide cannot be formed. Therefore, the orientation in the c-axis is essential.
Further, there was reported that when the tungsten bronze structure metal oxide is oriented, the high anisotropy causes a crack due to the high anisotropic shape. Non-patent Literature 1 discloses that for the purpose of preventing the crack, the high anisotropy is weakened by doping of La to prevent the occurrence of the crack. However, this method suffers from such a problem that the orientation is degraded, and the piezoelectric property is also deteriorated.